Generally the electric door operator is provided with a pull chain in addition to the electric actuating means for manually operating to roll up the shutter upon the failure of the electromotor or the interruption of service. FIG. 1 shows a door operator 1 conventionally used in orient countries, which is constituted of a pull chain disc 11, an electromotor 12 and a reduction gear box 13 in a sequence from the right to the left. The actuating force of the electromotor 12 is transmitted through the reduction gear box 13 to an output end 131 to roll the reel to close or open the shutter. Upon the failure of the electromotor or the interruption of service, a pull chain 111 is manually pulled to turn the rotating shaft of the electromotor 12 to roll the curtain slats. Since the pull chain disk 11 is provided on the outer end of the electromotor 12, when the electromotor 12 is disassembled for the purpose of maintenance, the pull chain 11 will be disassembled simultaneously, as a result of which the shutter cannot be closed or opened. Or, as found in the available door operator such as a door operator 1a is manufactured by Raynor Garage Doors of Illinois, USA as shown in FIG. 2 and a door operator 1b manufactured by Wayne-Dalton Corporation of Ohio, USA as shown in FIG. 3 the manual pull chain requires a manual pull rod for switching to a manual operation and hence it is inconvenient. Respectively as shown in FIGS. 2 and 3, the actuating force of electromoter 12a, 12b is transmitted through reduction gear boxes 13a, 13b which change axial direction at 90 degree to output ends 131a, 131b to roll the reel to close or open the shutter. Though upon the failure of the electromotors 12a, 12b or the interruption of service, pull chains 111a, 111b may be manually pulled to roll the reel to wind the shutter, it is inconvenient in usage due to the need of another hand to draw the pull chain 14a, 14b to switch to a manual operation.